In wireless data networks, mobile stations must generally request a data channel assignment before transmitting data. In the CDMA 2000 protocol, for example, the mobile station (MS) requests a data channel assignment by sending a Supplemental Channel Request Message (SCRM) to the network indicating how much data the MS has in its buffer. The channel assignment message from the network in the CDMA 2000 protocol is a Supplemental Channel Assignment Message (SCAM) or an Enhanced Supplemental Channel Assignment Message (ESCAM), which includes more information. The E/SCAM includes a scheduling period over which the MS may transmit data at an assigned data rate. In the existing CDMA 2000 protocol, the data channel request and assignment messaging occurs at Layer 3 in the architecture.
In the 3rd Generation Partnership Project 2 (3GPP2), Technical Specification Group C (TSG-C) Work Group 3 (WG3) has proposed an alternative data scheduling and rate control scheme including overhead channels that may replace the existing E/SCAM. In prior art FIG. 1, under the WG3 proposal, in response to a request message 110 from the MS on the reverse link (RL), the network transmits a scheduling (grant) message 120 on a forward link (FL) Grant Channel (F-GCH). The grant message assigns a data rate, e.g. 76.8 kbits/s, for the MS to transmit one encoder packet. Thereafter, upon successfully transmitting the encoder packet, the MS may continue to transmit data subject to a rate control command sent by the network on the forward link. The rate control command permits the network to adjust the data rate up or down one step at a time, e.g., 1 bit per 10 ms frame. The rate control command is sent prior to the frame whose rate it will control. In FIG. 1, the rate control command (RC) 130 sent during frame 140 controls the rate on future frame 142, RC 132 sent during frame 142 controls the rate of frame 144, etc. In the proposed scheme, the data rate may be maintained from one frame to the next.
An alternative proposal by 3GPP2 TSG-C WG3 is a modified grant message having an additional bit to disable the rate control command after transmitting one encoder packet. The effect of disabling the rate command enables the network to limit the data channel assignment to the one encoder packet. Thus, the MS must request a new data channel assignment for transmitting packets in addition to the original encoder packet.
In the existing CDMA 2000 data channel assignment protocol, the channel assignment is for a fixed period starting at a specified time. In the TSG-C WG3 proposals discussed above, the channel assignment is lost when there is a gap in transmission. FIG. 1 illustrates loss of the channel assignment upon completion of the transmission of data in frame 144, e.g., when the MS buffer is emptied, or upon discontinuous transmission (DTX), e.g., for lack of sufficient transmission power due to channel fading. In FIG. 1, data transmission resumes in frame 146 only upon receipt of a new grant 122 in response to a new request 112 transmitted by the MS on the reverse link. Cumulative channel assignment negotiation generally has an adverse impact on reverse and forward link capacity and may result latency. The CDMA 2000 protocol permits the MS to transmit data without a channel assignment, but the data rate is relatively low, on the theory that the network has inadequate forewarning, which is necessary to allocate resources to accommodate the transmission.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below.